Transcriptional Regulation of Indian Hedgehog Expression in Chondrocytes

软骨细胞中 Indian Hedgehog 表达的转录调控

• 批准号: 7843585
• 负责人: XIANGLI YANG
• 金额: $ 33.43万
• 依托单位: VANDERBILT UNIVERSITY
• 依托单位国家: 美国
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-08-15 至 2013-05-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7843585
• 关键词: Address; Agonist; BMP2 gene; Binding; Biochemical; Biological; Biological Assay; Biology; Bone Regeneration; CREB1 gene; Cartilage; Chondrocytes; Chondrogenesis; Coffin-Lowry syndrome; Defect; Degenerative polyarthritis; Disease; Elements; Epiphysial cartilage; Erinaceidae; Family; Figs - dietary; Fracture; Gene Expression; Gene Targeting; Genetic; Genetic Transcription; Human; Hypertrophy; Impairment; In Vitro; Investigation; Leucine Zippers; Limb Development; Limb structure; Link; Mental Retardation; Molecular; Molecular Genetics; Mus; Mutant Strains Mice; Mutate; Nuclear Extract; Organ Culture Techniques; Osteogenesis; Parathyroid Hormone Receptor; Parathyroid Hormone Receptors; Pathway interactions; Phenotype; Phosphorylation; Process; Protein Kinase; Proteins; Regulation; Role; Signal Transduction; Skeletal Development; Staging; System; Testing; Transactivation; Transcriptional Regulation; Transgenic Mice; Vascular Endothelial Growth Factors; Yang; base; improved; in utero; in vivo; mineralization; morphogens; mouse model; novel; osteoblast differentiation; overexpression; parathyroid hormone-related protein; premature; promoter; public health relevance; purmorphamine; receptor; repaired; skeletal; smoothened signaling pathway; transcription factor

Description (provided by applicant): During endochondral bone formation, osteogenesis and chondrogenesis are linked and highly coordinated. However, the regulatory mechanisms responsible for coordinating osteogenesis and chondrogenesis remain unclear. Genetic mouse models have shown that the Hedgehog (Hh) pathway, which controls target genes in chondrogenesis such as PTHrP and osteogenesis such as BMP2, is essential for normal endochondral bone formation. However, despite its obvious importance, little is known of the regulatory mechanisms that are responsible for controlling Hedgehog signaling. This proposal is directed at improving understanding of the transcriptional control of the Hedgehog pathway, and specifically of Ihh, during chondrogenesis and how it may be linked to osteogenesis. Since chondrocyte differentiation occurs also at early stages of cartilage degeneration as well as during bone regeneration, this study is directly applicable to diseases such as osteoarthritis and fractures. We hypothesize that the transcription factor ATF4 is a major regulator of Hedgehog signaling during chondrogenesis, and possibly during osteogenesis as well. Further, we hypothesize that ATF4 is a direct regulator of Ihh transcription. We base this hypothesis on the following rationale. 1. We have found that ATF4 is essential for osteoblast differentiation and bone formation (Yang, et al., 2004). 2. Atf4-deficient (Atf4-/-) mice are dwarfs, suggesting a defect in growth plate chondrocytes. 3. Atf4-/- growth plate chondrocytes show several abnormalities including a delay in hypertrophic mineralization, an expansion of the hypertrophic zone, and most notably a decrease in Ihh gene expression and proliferation. These defects are reminiscent of the Ihh-/-, PPR-/-(receptor for parathyroid hormone, PTH, and PTH related protein, PTHrP), and PTHrP-/- limb phenotypes. 4. ATF4 transactivates Ihh through directly binding to a cis element of the Ihh promoter. 5. Activation of Ihh signaling restores the size of in Atf4-/- limb in an organ culture system. To test our hypothesis that ATF4 is a regulatory factor for Hedgehog signaling in chondrogenesis, we plan the following specific aims. 1. To determine the molecular mechanisms whereby ATF4 regulates Ihh transcription. 2. To address the role of ATF4 in regulating growth plate chondrocytes proliferation and differentiation in vivo. 3. To demonstrate that Ihh is a direct transcriptional target of ATF4 in vivo. PUBLIC HEALTH RELEVANCE. Indian hedgehog (Ihh) is a well-studied morphogen that regulates the coordination between chondrogenesis and osteogenesis, two processes during skeletal development and bone fracture repair. Surprisingly, investigations on the regulation of Ihh itself are lacking, particularly at the transcriptional level. In this proposal, we intend to investigate this important biological question through systematic molecular and genetic studies.

描述（申请人提供）：在软骨内成骨过程中，成骨和软骨形成是相互联系和高度协调的。然而，负责协调骨形成和软骨形成的调节机制仍不清楚。遗传小鼠模型显示，Hedgehog （Hh）通路控制软骨形成过程中的靶基因，如PTHrP和成骨过程中的靶基因，如BMP2，对正常的软骨内骨形成至关重要。然而，尽管它的重要性显而易见，但对控制Hedgehog信号传导的调控机制知之甚少。这一建议旨在提高对Hedgehog途径，特别是Ihh在软骨形成过程中的转录控制以及它如何与成骨相关的理解。由于软骨退行性变早期和骨再生阶段也发生软骨细胞分化，因此本研究直接适用于骨关节炎、骨折等疾病。我们假设转录因子ATF4是软骨形成过程中Hedgehog信号的主要调节因子，也可能在成骨过程中。此外，我们假设ATF4是Ihh转录的直接调节剂。我们的假设基于以下基本原理。1. 我们发现ATF4对成骨细胞分化和骨形成至关重要（Yang等，2004）。2. Atf4缺陷（Atf4-/-）小鼠矮化，提示生长板软骨细胞缺陷。3. Atf4-/-生长板软骨细胞表现出几种异常，包括肥厚矿化延迟，肥厚带扩大，最明显的是Ihh基因表达和增殖减少。这些缺陷让人想起Ihh-/-， PPR-/-（甲状旁腺激素，PTH和PTH相关蛋白的受体，PTHrP）和PTHrP-/-肢体表型。4. ATF4通过直接结合Ihh启动子的顺式元件来激活Ihh。5. 激活Ihh信号可以恢复器官培养系统中Atf4-/-肢体的大小。为了验证我们的假设，即ATF4是Hedgehog信号在软骨形成中的调节因子，我们计划以下具体目标。1. 确定ATF4调控Ihh转录的分子机制。2. 探讨ATF4在体内调节生长板软骨细胞增殖分化中的作用。3. 在体内证明Ihh是ATF4的直接转录靶点。公共卫生相关性。印度刺猬（Ihh）是一种被广泛研究的形态因子，它调节骨骼发育和骨折修复过程中软骨形成和成骨形成之间的协调。令人惊讶的是，缺乏对Ihh本身调控的研究，特别是在转录水平上。在本提案中，我们打算通过系统的分子和遗传学研究来研究这一重要的生物学问题。